1. Field of the Invention
The present invention relates to an active distance measuring apparatus for projecting modulated light to an object and measuring distance to said object from the light reflected therefrom.
2. Related Background Art
In the field of such apparatus, an active distance measuring apparatus for projecting pulse modulated infrared light to an object and receiving the reflected light from the object by a photosensor is disclosed for example in the Japanese Patent Publication 58-42411. For use as such photosensor there is known a position sensor device (PSD) providing photocurrents I.sub.1, I.sub.2 from a pair of output electrodes according to the incident position of the reflected light.
In such distance measuring apparatus, alternating photocurrents I.sub.1, I.sub.2 of a frequency equal to that of the pulse modulated light are converted into DC signals by a synchronized rectifying amplifier and subjected to addition and subtraction, and the added value (I.sub.1 +I.sub.2 and the subtracted value (I.sub.1 -I.sub.2) are amplified by DC amplifiers and are used for calculating distance data L according to the following equation: ##EQU1## wherein .alpha. is a constant.
Thus the distance data contain errors due to offsets and drifts in various amplifiers, for example the DC amplifier after rectification.